Cell cycle dysregulation is a central mechanism in carcinogenesis. Oncogenes and tumor suppressors exert their ultimate mode of action by impinging at strategic points in the cell cycle. Tumor-associated genes interact with key cell cycle regulators in tumor promotion and tumor suppression. The proposed fellowship training provides opportunities for the applicant to examine the molecular, biological, and functional interactions of a recently identified growth suppressor protein, p12(DOC-1), and the cell cycle regulator cyclin-dependent kinase 2 (CDK2), in cell cycle control and oral carcinogenesis. p12(DOC-1) is a growth suppressor identified by differential gene expression screening between normal and malignant oral keratinocytes. p12(DOC-1) negatively regulates DNA replication by associating and mediating phosphorylation of the catalytic subunit of DNA-polymerase alpha/primase (DNA-PP), implicated in the termination mechanism of DNA replication at the end of S phase. Data will be presented to show that p12(DOC-1) interacts with CDK2, a regulator of G1/S transition, S phase progression and DNA replication. We hypothesize that p12(DOC- 1) interacts with CDK2 in cell cycle control and tumor suppression. This hypothesis will be tested by the following three specific aims: 1. to examine the molecular interactions of p12(DOC-1) with CDK2; 2. to examine the interactions of p12(DOC-1) with CDK2 in cell cycle control and 3. to examine the interactions of p12(DOC-1) with CDK2 in oral cancer. The outcome of the proposed work will advance our understanding of cell cycle control and oral carcinogenesis by examining mechanisms of interactions of a novel cell cycle regulator p12(DOC-1) with the well- studied S phase regulator, CDK2.